U.S. patent application number 11/221710 was filed with the patent office on 2007-03-22 for technique for atomic layer deposition.
Invention is credited to Jeffrey A. Hopwood, Harold M. Persing, Anthony Renau, Vikram Singh, Edmund J. Winder.
Application Number | 20070065576 11/221710 |
Document ID | / |
Family ID | 37884490 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070065576 |
Kind Code |
A1 |
Singh; Vikram ; et
al. |
March 22, 2007 |
Technique for atomic layer deposition
Abstract
A technique for atomic layer deposition is disclosed. In one
particular exemplary embodiment, the technique may be realized by
an apparatus for atomic layer deposition. The apparatus may
comprise a process chamber having a substrate platform to hold at
least one substrate. The apparatus may also comprise a supply of a
precursor substance, wherein the precursor substance comprises
atoms of at least one first species and atoms of at least one
second species, and wherein the supply provides the precursor
substance to saturate a surface of the at least one substrate. The
apparatus may further comprise a plasma source of metastable atoms
of at least one third species, wherein the metabstable atoms are
capable of desorbing the atoms of the at least one second species
from the saturated surface of the at least one substrate to form
one or more atomic layers of the at least one first species.
Inventors: |
Singh; Vikram; (North
Andover, MA) ; Persing; Harold M.; (Rockport, MA)
; Winder; Edmund J.; (Waltham, MA) ; Hopwood;
Jeffrey A.; (Needham, MA) ; Renau; Anthony;
(West Newbury, MA) |
Correspondence
Address: |
HUNTON & WILLIAMS LLP;INTELLECTUAL PROPERTY DEPARTMENT
1900 K STREET, N.W.
SUITE 1200
WASHINGTON
DC
20006-1109
US
|
Family ID: |
37884490 |
Appl. No.: |
11/221710 |
Filed: |
September 9, 2005 |
Current U.S.
Class: |
427/248.1 ;
118/715; 118/723R |
Current CPC
Class: |
C23C 16/452 20130101;
C23C 16/45544 20130101; C23C 16/45546 20130101; C23C 16/4554
20130101 |
Class at
Publication: |
427/248.1 ;
118/715; 118/723.00R |
International
Class: |
C23C 16/00 20060101
C23C016/00 |
Claims
1. An apparatus for atomic layer deposition, the apparatus
comprising: a process chamber having a substrate platform to hold
at least one substrate; a supply of a precursor substance, wherein
the precursor substance comprises atoms of at least one first
species and atoms of at least one second species, and wherein the
supply provides the precursor substance to saturate a surface of
the at least one substrate; and a plasma source of metastable atoms
of at least one third species, wherein the metabstable atoms are
capable of desorbing the atoms of the at least one second species
from the saturated surface of the at least one substrate to form
one or more atomic layers of the at least one first species.
2. The apparatus according to claim 1 further comprising one or
more devices for preventing at least a portion of charged particles
generated in the plasma source from reaching the substrate
surface.
3. The apparatus according to claim 1, wherein the substrate
platform is so oriented as to prevent at least a portion of charged
particles generated in the plasma source from reaching the
substrate surface.
4. The apparatus according to claim 1 further comprising a supply
of a dopant precursor, wherein the supply of the dopant precursor
is configured to substitute the supply of the precursor substance
in one or more deposition cycles, thereby doping the one or more
atomic layers of the at least one first species.
5. The apparatus according to claim 1 further comprising a supply
of a dopant precursor, wherein, in one or more deposition cycles,
the supply of the dopant precursor is configured to supply the
dopant precursor at substantially the same time when the supply of
the precursor substance supplies the precursor substance, thereby
doping the one or more atomic layers of the at least one first
species.
6. The apparatus according to claim 1, wherein the plasma source of
metastable atoms further comprises a plasma chamber coupled to the
process chamber, the plasma chamber being adapted to generate the
metastable atoms of the at least one third species.
7. The apparatus according to claim 6, wherein the plasma chamber
generates the metastable atoms of the at least one third species
from an inductively coupled plasma.
8. The apparatus according to claim 1, wherein the precursor
substance comprises one or more species selected from a group
consisting of: silicon; carbon; germanium; gallium; arsenic;
indium; aluminum; and phosphorus.
9. The apparatus according to claim 1, wherein the substrate
surface comprises one or more materials selected from a group
consisting of: silicon; silicon-on-insulator (SOI); silicon
dioxide; diamond; silicon germanium; silicon carbide; a III-V
compound; a flat panel material; a polymer; and a flexible
substrate material.
10. The apparatus according to claim 1, wherein the at least one
third species comprises one or more species selected from a group
consisting of: helium (He); neon (Ne); argon (Ar); krypton (Kr);
radon (Rn); and xenon (Xe).
11. The apparatus according to claim 1, wherein the at least one
substrate is kept at a temperature below 500.degree. C.
12. A method for atomic layer deposition, the method comprising the
steps of: saturating a substrate surface with a precursor substance
having atoms of at least one first species and atoms of at least
one second species, thereby forming a monolayer of the precursor
substance on the substrate surface; and exposing the substrate
surface to plasma-generated metastable atoms of a third species,
wherein the metastable atoms desorb the atoms of the at least one
second species from the substrate surface to form an atomic layer
of the at least one first species.
13. An atomic layer deposition method comprising multiple
deposition cycles to form a plurality of atomic layers of the first
species, wherein each deposition cycle repeats the steps as recited
in claim 12 to form one atomic layer of the first species.
14. The method according to claim 13, further comprising: supplying
the substrate surface with a dopant precursor, concurrently with a
supply of the precursor substance, in one or more of the multiple
deposition cycles to dope the plurality of atomic layers of the at
least one first species.
15. The method according to claim 13, further comprising:
substituting the precursor substance with a dopant precursor in one
or more of the multiple deposition cycles to dope the plurality of
atomic layers of the at least one first species.
16. The method according to claim 13, further comprising:
preventing at least a portion of charged particles generated in a
plasma source of the metastable atoms from reaching the substrate
surface.
17. The method according to claim 13, further comprising: annealing
the substrate surface at a temperature below 500.degree. C.
18. The method according to claim 13, wherein: the precursor
substance comprises disilane (Si.sub.2H.sub.6); the at least one
first species comprises silicon; the at least one second species
comprises hydrogen; and the third species comprises helium.
19. The method according to claim 18, further comprising: masking
one or more selected portions of the substrate surface with silicon
dioxide (SiO.sub.2).
20. The method according to claim 13, wherein the precursor
substance comprises one or more species selected from a group
consisting of: silicon; carbon; germanium; gallium; arsenic;
indium; aluminum; and phosphorus.
21. The method according to claim 13, wherein the substrate surface
comprises one or more materials selected from a group consisting
of: silicon; silicon-on-insulator (SOI); silicon dioxide; diamond;
silicon germanium; silicon carbide; a III-V compound; a flat panel
material; a polymer; and a flexible substrate material.
22. The method according to claim 13, wherein the at least one
third species comprises one or more species selected from a group
consisting of: helium (He); neon (Ne); argon (Ar); krypton (Kr);
radon (Rn); and xenon (Xe).
23. An apparatus for atomic layer deposition, the apparatus
comprising: a process chamber having a substrate platform to hold
at least one substrate; a supply of disilane (Si.sub.2H.sub.6),
wherein the supply is adapted to supply a sufficient amount of
disilane to saturate a surface of the at least one substrate; a
supply of helium; and a plasma chamber coupled to the process
chamber, the plasma chamber being adapted to generate helium
metastable atoms from helium supplied by the supply of helium;
wherein the metabstable atoms are capable of desorbing hydrogen
atoms from the saturated surface of the at least one substrate,
thereby forming one or more atomic layers of silicon.
24. The apparatus according to claim 23, further comprising a
supply of diborane (B.sub.2H.sub.6), wherein the supply of diborane
is configured to substitute at least a portion of the supply of
disilane in one or more deposition cycles, thereby introducing
boron atoms to the one or more atomic layers of silicon.
25. A method of conformal doping comprising: forming a thin film on
a substrate surface in one or more deposition cycles, wherein, in
each of the one or more deposition cycles, a precursor substance
having atoms of at least one first species and atoms of at least
one second species is supplied to saturate the substrate surface,
and then the atoms of the at least one second species are desorbed
from the saturated substrate surface to form one or more atomic
layers of the at least one first species; and substituting, in one
or more of the multiple deposition cycles, at least a portion of
the supply of the precursor substance with a dopant precursor,
thereby doping the one or more atomic layers of the at least one
first species.
26. The method according to claim 25, wherein the atoms of the at
least one second species are desorbed with metastable atoms of at
least one third species.
27. The method according to claim 25, wherein the metastable atoms
of the at least one third species are generated with a plasma.
28. The method according to claim 27, wherein at least a portion of
charged particles are prevented from reaching the substrate
surface.
29. The method according to claim 27, wherein the at least one
third species comprises one or more species selected from a group
consisting of: helium (He); neon (Ne); argon (Ar); krypton (Kr);
radon (Rn); and xenon (Xe).
30. The method according to claim 25, wherein the precursor
substance comprises one or more species selected from a group
consisting of: silicon; carbon; germanium; gallium; arsenic;
indium; aluminum; and phosphorus.
31. The method according to claim 25, wherein the substrate surface
comprises one or more materials selected from a group consisting
of: silicon; silicon-on-insulator (SOI); silicon dioxide; diamond;
silicon germanium; silicon carbide; a III-V compound; a flat panel
material; a polymer; and a flexible substrate material.
32. The method according to claim 25, wherein the substrate surface
is kept at a temperature below 500.degree. C.
33. The method according to claim 25, wherein the substrate surface
is not subject to a further thermal process that re-distributes
atoms of the dopant precursor.
34. The method according to claim 25, wherein the substrate surface
has a three-dimensional topology and the thin film is conformally
formed and conformally doped thereon.
35. The method according to claim 34, wherein the thin film is part
of a FinFET structure.
Description
FIELD OF THE DISCLOSURE
[0001] The present disclosure relates generally to semiconductor
manufacturing and, more particularly, to a technique for atomic
layer deposition.
BACKGROUND OF THE DISCLOSURE
[0002] Modern semiconductor manufacturing has created a need for
precision, atomic-level deposition of high quality thin film
structures. Responsive to this need, a number of film growth
techniques collectively known as "atomic layer deposition" (ALD) or
"atomic layer epitaxy" (ALE) have been developed in recent years.
ALD technology is capable of depositing uniform and conformal films
with atomic layer accuracy. A typical ALD process uses sequential
self-limiting surface reactions to achieve control of film growth
in the monolayer thickness regime. Due to its excellent potential
for film conformity and uniformity, ALD has become the technology
of choice for advanced applications such as high dielectric
constant (high-k) gate oxide, storage capacitor dielectrics, and
copper diffusion barriers in microelectronic devices. In fact, ALD
technology may be useful for any advanced application that benefits
from precise control of thin film structure on the nanometer (nm)
or sub-nanometer scale.
[0003] To date, however, most existing deposition techniques suffer
from inherent deficiencies and have not been reliably applied to
mass production in the semiconductor industry. For example, a
deposition technique known as "molecular beam epitaxy" (MBE) uses
shutter-controlled individual effusion cells to direct atoms of
different species towards a substrate surface, on which these atoms
react with each other to form a desired monolayer. In a
solid-source MBE process, the effusion cells have to be heated to
considerably high temperatures for thermionic emission of the
ingredient atoms. In addition, extremely high vacuum has to be
maintained to ensure no collision among the ingredient atoms before
they reach the substrate surface. Despite the high temperature and
high vacuum requirement, MBE film growth rates are quite low for
mass production purposes.
[0004] Another ALD technique is known as temperature-modulated
atomic layer epitaxy (ALE). To grow a silicon film according to
this technique, the following steps are repeated. First, a
monolayer of silane (SiH.sub.4) is deposited on a substrate surface
at a relatively low temperature between 180.degree. C. and
400.degree. C. Then, the substrate temperature is ramped to
approximately 550.degree. C. to desorb the hydrogen atoms, leaving
behind a monolayer of silicon. Although this technique does achieve
a controlled layer-by-layer film growth, the requirement for
repeated temperature spikes makes it difficult to maintain
uniformity across large wafers and repeatability from layer to
layer. Additionally, heating the substrate to high temperatures can
damage or destroy delicate structures formed on the substrate in
previous processing steps.
[0005] One existing ALD technique employs ion bombardment to desorb
excess hydrogen atoms. According to this technique, a disilane
(Si.sub.2H.sub.6) gas may be used to form a disilane monolayer on a
substrate surface. The substrate surface is then bombarded with
helium or argon ions to desorb excess hydrogen atoms from the
disilane monolayer to form a silicon monolayer. Perhaps due to
overly energetic ion bombardments (.about.50 eV ion energy), the
film growth rate is fairly low (less than 0.15 monolayer per
cycle), and energetic ion fluxes are essentially line-of-sight
processes which therefore can compromise atomic layer deposition's
potential for a highly conformal deposition. Further, the energetic
ion can also cause crystalline defects which may necessitate
post-deposition annealing.
[0006] Further, conformal doping for ALD-deposited thin films,
especially in 3-D structures (e.g., FinFETs), remains a challenge
to process engineers. Existing ion implantation techniques are
undesirable for introducing dopants into a 3-D conformally covered
structure, not only because it is hard to achieve uniformity of
dopant distribution, but also due to the potential damages that may
result from a post-implant anneal.
[0007] In view of the foregoing, it would be desirable to provide
an atomic layer deposition solution which overcomes the
above-described inadequacies and shortcomings.
SUMMARY OF THE DISCLOSURE
[0008] A technique for atomic layer deposition is disclosed. In one
particular exemplary embodiment, the technique may be realized by
an apparatus for atomic layer deposition. The apparatus may
comprise a process chamber having a substrate platform to hold at
least one substrate. The apparatus may also comprise a supply of a
precursor substance, wherein the precursor substance comprises
atoms of at least one first species and atoms of at least one
second species, and wherein the supply provides the precursor
substance to saturate a surface of the at least one substrate. The
apparatus may further comprise a plasma source of metastable atoms
of at least one third species, wherein the metabstable atoms are
capable of desorbing the atoms of the at least one second species
from the saturated surface of the at least one substrate to form
one or more atomic layers of the at least one first species.
[0009] In another particular exemplary embodiment, the technique
may be realized as a method for atomic layer deposition. The method
may comprise saturating a substrate surface with a precursor
substance having atoms of at least one first species and atoms of
at least one second species, thereby forming a monolayer of the
precursor substance on the substrate surface. The method may also
comprise exposing the substrate surface to plasma-generated
metastable atoms of a third species, wherein the metastable atoms
desorb the atoms of the at least one second species from the
substrate surface to form an atomic layer of the at least one first
species. An atomic layer deposition method may comprise multiple
deposition cycles to form a plurality of atomic layers of the first
species, wherein each deposition cycle repeats the steps as recited
above to form one atomic layer of the first species.
[0010] In yet another particular exemplary embodiment, the
technique may be realized by an apparatus for atomic layer
deposition. The apparatus may comprise a process chamber having a
substrate platform to hold at least one substrate. The apparatus
may also comprise a supply of disilane (Si.sub.2H.sub.6), wherein
the supply is adapted to supply a sufficient amount of disilane to
saturate a surface of the at least one substrate, a supply of
helium. The apparatus may further comprise a plasma chamber coupled
to the process chamber, the plasma chamber being adapted to
generate helium metastable atoms from helium supplied by the supply
of helium. The metabstable atoms may be capable of desorbing
hydrogen atoms from the saturated surface of the at least one
substrate, thereby forming one or more atomic layers of
silicon.
[0011] In still another particular exemplary embodiment, the
technique may be realized as a method of conformal doping. The
method may comprise forming a thin film on a substrate surface in
one or more deposition cycles, wherein, in each of the one or more
deposition cycles, a precursor substance having atoms of at least
one first species and atoms of at least one second species is
supplied to saturate the substrate surface, and then the atoms of
the at least one second species are desorbed from the saturated
substrate surface to form one or more atomic layers of the at least
one first species. The method may also comprise substituting, in
one or more of the multiple deposition cycles, at least a portion
of the supply of the precursor substance with a dopant precursor,
thereby doping the one or more atomic layers of the at least one
first species.
[0012] The present disclosure will now be described in more detail
with reference to exemplary embodiments thereof as shown in the
accompanying drawings. While the present disclosure is described
below with reference to exemplary embodiments, it should be
understood that the present disclosure is not limited thereto.
Those of ordinary skill in the art having access to the teachings
herein will recognize additional implementations, modifications,
and embodiments, as well as other fields of use, which are within
the scope of the present disclosure as described herein, and with
respect to which the present disclosure may be of significant
utility.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] In order to facilitate a fuller understanding of the present
disclosure, reference is now made to the accompanying drawings, in
which like elements are referenced with like numerals. These
drawings should not be construed as limiting the present
disclosure, but are intended to be exemplary only.
[0014] FIG. 1 shows a block diagram illustrating an exemplary
atomic layer deposition cycle in accordance with an embodiment of
the present disclosure.
[0015] FIG. 2 shows a block diagram illustrating an exemplary
atomic layer deposition cycle in accordance with an embodiment of
the present disclosure.
[0016] FIG. 3 shows a block diagram illustrating an exemplary
system for atomic layer deposition in accordance with an embodiment
of the present disclosure.
[0017] FIG. 4 shows a flow chart illustrating an exemplary method
for atomic layer deposition in accordance with an embodiment of the
present disclosure.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0018] To solve the aforementioned problems associated with
existing atomic layer deposition techniques, embodiments of the
present disclosure introduce an ALD and in situ doping technique.
Metastable atoms may be used to desorb excess atoms. The metastable
atoms may be generated, for example, in a plasma chamber. For
illustration purposes, the following description will focus on a
method and apparatus for depositing doped or undoped silicon using
helium metastable atoms. It should be appreciated that, with a same
or similar technique, thin films of other species may also be grown
using helium or other metastable atoms.
[0019] Referring to FIG. 1, there is shown a block diagram
illustrating an exemplary atomic layer deposition cycle 100 in
accordance with an embodiment of the present disclosure. The
exemplary atomic layer deposition cycle 100 may comprise two
phases, a saturation phase 10 and a desorption phase 12.
[0020] In the saturation phase 10, a substrate 102 may be exposed
to a disilane (Si.sub.2H.sub.6) gas. For silicon film growth, the
substrate surface may comprise, for example, silicon,
silicon-on-insulator (SOI), and/or silicon dioxide. The disilane
gas serves as a silicon precursor, and is supplied in a
sufficiently high dose to saturate the substrate surface forming a
disilane monolayer 104 thereon. Throughout this disclosure,
however, use of the word "saturate" does not preclude the scenario
where a substrate surface is only partially covered by a substance
used to "saturate" such surface. The substrate 102 as well as the
process environment may be kept at a carefully selected temperature
to prevent the precursor gas from condensing or decomposing on the
substrate surface. In this embodiment, the substrate 102 is heated
to and maintained at a temperature between 180.degree. C. and
400.degree. C., although it is within the scope of the present
disclosure to heat and maintain the substrate 102 within other
temperature ranges.
[0021] In the desorption phase 12, the substrate 102 may be exposed
to metastable atoms with sufficient energy to desorb the excess
atoms from the precursor monolayer. According to this embodiment,
helium metastable atoms may be used to desorb excess hydrogen
atoms, either partially or completely, from the disilane monolayer
104 formed in the saturation phase 10. The helium metastable atoms
may be created, for example, from a helium gas in an inductively
coupled plasma. Each helium metastable atom may have an internal
energy of approximately 20 eV, which can be used to break the bond
between a silicon atom and a hydrogen atom. According to some
embodiments, the metastable and other excited states of an inert
gas (helium, argon, etc.) tend to emit photons that may also
indirectly drive the desorption reactions at the substrate surface.
After the excess hydrogen atoms have been removed, a silicon
monolayer 106 may be formed on the substrate surface. According to
some embodiments, not all of the excess hydrogen atoms may be
removed. Therefore, at the end of the desorption phase 12, the
surface of the silicon monolayer 106 may be a mixture of dangling
bonds and hydrogen-terminated silicon atoms.
[0022] Between the saturation phase 10 and the desorption phase 12,
the substrate surface may be purged with one or more inert gases
(e.g., helium or argon) to remove the excess reaction gases as well
as by-products (e.g., hydrogen). A complete cycle through the
saturation phase 10 and the desorption phase 12, including the
"purge" steps between the two phases, may be referred to as one
"deposition cycle." The deposition cycle 100 may be repeated to
form a thin film of pure silicon (e.g., crystalline,
polycrystalline, amorphous type, etc.), one monolayer (or
fractional monolayer) at a time.
[0023] According to embodiments of the present disclosure, it may
be advantageous to use metastable atoms rather than ions to desorb
excess atoms from a substrate surface saturated with a precursor
substance. Where the metastable atoms are generated in a plasma for
desorption purposes, it may be desirable to prevent charged
particles (e.g., electrons and ions) generated in the plasma from
reaching the substrate surface, such that anisotropic film
properties due to these charged particles may be reduced or
minimized. A number of measures may be taken to prevent charged
particles from affecting the ALD film formed on the substrate
surface. For example, one or more devices (e.g., a baffle or
screen) may be interposed between the plasma source and the
substrate. These devices may further be biased filter out unwanted
charged particles. Alternatively, an electromagnetic field may be
set up to deflect charge particles. According to other embodiments,
the orientation of the substrate surface may be adjusted to
minimize the incident influx of charged particles. For example, the
substrate platform may be inverted or otherwise turned away from
the line of sight of the plasma source. Alternatively, the plasma
source may be positioned at a distance from the substrate so as to
cause a significant portion of the charged particles to fail to
reach the substrate surface due to scattering or collisions.
[0024] Referring to FIG. 2, there is shown a block diagram
illustrating an exemplary atomic layer deposition cycle 200 in
accordance with another embodiment of the present disclosure.
According to this embodiment, the ALD process as illustrated in
FIG. 1 above may be utilized not only to deposit a single-species
thin film, but also to introduce impurities into the thin film or
to form a multi-species and/or alternate-layered film, all in a
well controlled manner. For example, apart from an undoped silicon
film, a doped silicon film may also be grown based on a slightly
modified ALD process. According to this modified ALD process, one
or more deposition cycles 100 may be replaced with one or more
deposition cycles 200.
[0025] In a saturation phase 20 of a deposition cycle 200, a dopant
precursor gas may be provided in place of or concurrently with the
silicon precursor gas. In the exemplary embodiment illustrated in
FIG. 2, the dopant precursor is diborane (B.sub.2H.sub.6) which may
adsorb (or "chemisorb") to the surface of the substrate 102 to form
a diborane monolayer 204. The underlying surface, in this case, may
comprise a silicon monolayer deposited in a previous deposition
cycle 100. The diborane monolayer 204 may partially or completely
cover the underlying surface.
[0026] In a desorption phase 22 of a deposition cycle 200, the
substrate 102 may be exposed to helium metastable atoms as
described above. The helium metastable atoms may desorb excess
hydrogen atoms from the diborane monolayer 204, leaving behind a
partial or complete boron monolayer 206.
[0027] By controlling the number of deposition cycles 100 to be
replaced with the deposition cycle 200, and by controlling the dose
of diborane gas supplied in the saturation phase 20, a desired
boron dopant density profile in the silicon film may be achieved.
Since this in situ doping technique relies on conformal deposition
of dopant atoms rather than ion implantation, it may achieve a
uniform dopant distribution over the complex surface of a 3-D
structure such as a FinFET. Further, there is no need for a
post-deposition high-temperature diffusion process as required for
ion implanted dopant atoms. Instead, no annealing or only a
low-temperature annealing is needed, which results in reduced
diffusion of the dopant species and therefore very abrupt (or
"box-like") dopant profiles. As such, embodiments of the present
disclosure may be implemented at temperatures below 500.degree. C.,
which is well within the semiconductor industry's "thermal
budget."
[0028] The atomic layer deposition in accordance with embodiments
of the present disclosure may be a selective process depending on
the substrate surface composition. For example, the process
illustrated in FIG. 1 may deposit silicon monolayers on a silicon
or SOI surface but not on a silicon dioxide (SiO.sub.2) surface.
Thus, silicon dioxide may be used as a masking layer to shield
selected portions of the substrate surface.
[0029] It should be appreciated that, although only helium
metastable atoms are used in the above examples, atoms of other
species may also be chosen for the desorption process. Choice of
these species may be based on the lifetime and energy of their
metastable or excited states. Table 1 provides a list of candidate
species whose metastable atoms may be used in the desorption phase
of an ALD process. TABLE-US-00001 TABLE 1 Species Lifetime (s)
Energy (eV) He 8000 19.8 Ne 24 17 Ar 40 12 Kr 30 10 Xe 43 8.4
[0030] It should also be appreciated that, apart from a diborane
gas, other dopant precursors may also be used to introduce desired
dopant atoms into ALD-formed thin films. Suitable dopant precursors
for introducing dopant atoms such as boron (B), arsenic (As),
phosphorus (P), indium (In), and antimony (Sb) may include but are
not limited to the following classes of compounds: halides (e.g.,
BF.sub.3), alkoxides (e.g., B(OCH.sub.3).sub.3), alkyls (e.g.,
In(CH.sub.3).sub.3), hydrides (e.g., AsH.sub.3, PH.sub.3),
cyclopentadienyls, alkylimides, alkylamides (e.g.,
P[N(CH.sub.3).sub.2] 3), and amidinates.
[0031] Further, the in situ doping technique, in which
dopant-containing monolayers are deposited through an ALD-like
process, is not limited to plasma-enhanced ALD processes. Nor does
this in situ doping technique require the use of metastable atoms.
For example, a thermal ALD process may also be adapted to form the
dopant-containing monolayers. In fact, this in situ doping concept
is applicable to any ALD process wherein one or more deposition
cycles that deposit the monolayers of the thin film to be doped may
be replaced with one or more deposition cycles that deposit the
dopant-containing monolayers, or wherein the thin film to be doped
may be deposited in substantially the same time as the
dopant-containing monolayers.
[0032] FIG. 3 shows a block diagram illustrating an exemplary
system 300 for atomic layer deposition in accordance with an
embodiment of the present disclosure.
[0033] The system 300 may comprise a process chamber 302, which is
typically capable of a high vacuum base pressure (e.g.,
10.sup.-7-10.sup.-6 torr) with, for example, a turbo pump 306, a
mechanical pump 308, and other necessary vacuum sealing components.
Inside the process chamber 302, there may be a substrate platform
310 that holds at least one substrate 30. The substrate platform
310 may be equipped with one or more temperature management devices
to adjust and maintain the temperature of the substrate 30. Tilting
or rotation of the substrate platform 30 may also be accommodated.
The process chamber 302 may be further equipped with one or more
film growth monitoring devices, such as a quartz crystal
microbalance and/or a RHEED (reflection high energy electron
diffraction) instrument.
[0034] The system 300 may also comprise a plasma chamber 304 which
may be either coupled to or part of the process chamber 302. A
radio frequency (RF) power supply 312 may be used to generate an
inductively coupled plasma 32 inside the plasma chamber 304. For
example, a helium gas supplied with a proper pressure may be
excited by the RF power to generate a helium plasma which in turn
generates helium metastable atoms.
[0035] The system 300 may further comprise a number of gas
supplies, such as a disilane supply 314, a diborane supply 316, an
argon supply 318, and a helium supply 320. Each gas supply may
comprise a flow-control valve to set individual flow rates as
desired. Alternately, the gas may be metered into the system by a
series connection of, for example, a valve, a small chamber of
fixed volume, and a second valve. The small chamber is first filled
to the desired pressure by opening the first valve. After the first
valve is closed, the fixed volume of gas is released into the
chamber by opening the second valve. The disilane supply 314 and
the diborane supply 316 may be coupled to the process chamber 302
through a first inlet 322, and may supply a sufficient amount of
the respective silicon and boron precursor gases to saturate the
substrate 30. The argon supply 318 and the helium supply 320 may be
coupled to the plasma chamber 304 through a second inlet 324. The
argon supply 318 may provide argon (or other inert gases) to purge
the system 300. The helium supply 320 may supply a helium gas for
plasma generation of helium metastable atoms. Optionally, there may
be a screen or baffle device 326 between the plasma chamber 304 and
the process chamber 302. The screen or baffle device 326, either
biased or unbiased, may serve to prevent at least a portion of
charged particles generated in the plasma chamber 304 from reaching
the substrate 30.
[0036] FIG. 4 shows a flow chart illustrating an exemplary method
for atomic layer deposition in accordance with an embodiment of the
present disclosure.
[0037] In step 402, a deposition system such as the one shown in
FIG. 3 may be pumped down to a high-vacuum (HV) state. The vacuum
condition may be achieved with any vacuum technology whether now
known or later developed. The vacuum equipment may include, for
example, one or more of a mechanical pump, a turbo pump, and a cryo
pump. The vacuum level is preferably at least 10.sup.-7-10.sup.-6
torr, although it is within the scope of the present disclosure to
maintain the vacuum level at other pressures. For example, if a
higher film purity is desired, an even higher base vacuum may be
needed. For a low-purity film, a lower vacuum may be
acceptable.
[0038] In step 404, a substrate may be preheated to a desired
temperature. The substrate temperature may be determined based on
substrate type, ALD reaction species, desired growth rate, etc.
[0039] In step 406, a silicon precursor gas such as disilane (and
its carrier gas, if any) may be flowed into a process chamber where
the substrate sits. The silicon precursor gas may be supplied at a
flow rate or pressure sufficient to saturate the substrate surface.
The flow of disilane may last, for example, for a few seconds or up
to a few tens of seconds. A monolayer of disilane may partially or
completely cover the substrate surface.
[0040] In step 408, after surface saturation, the silicon precursor
may be turned off and the deposition system may be purged with one
or more inert gases to remove the excess silicon precursor.
[0041] In step 410, a helium plasma may be turned on. That is, a
helium gas may be flowed from a plasma chamber to the process
chamber. The helium plasma may be an inductively coupled plasma
(ICP) or any of a number of other plasma types that provide enough
excitation to the helium atoms to create helium metastable atoms.
The substrate in the process chamber may be exposed to the helium
metastable atoms so that they may react with the adsorbed silicon
precursor thereon to desorb the non-silicon atoms. For example, for
a disilane monolayer, the helium metastable atoms may help remove
the excess hydrogen atoms to form a desired silicon monolayer.
Exposure of the substrate surface to the metastable atoms may last,
for example, for a few seconds or up to a few tens of seconds.
[0042] In step 412, the helium plasma may be turned off and the
deposition system may be again purged with one or more inert
gases.
[0043] In step 414, it may be determined whether any doping of the
silicon film is desired. If doping is desired and it is an
appropriate time to introduce dopants, the process may branch to
step 416. Otherwise, the process may loop back to step 406 to start
depositing a next monolayer of silicon and/or finish depositing a
partial monolayer of silicon.
[0044] In step 416, a dopant precursor gas such as diborane (and
its carrier gas, if any) may be flowed into the process chamber.
The dopant precursor gas may be supplied at a flow rate or pressure
sufficient to saturate the substrate surface. The flow of diborane
may last, for example, for a few seconds or up to a few tens of
seconds. A monolayer of diborane may partially or completely cover
the substrate surface.
[0045] In step 418, after surface saturation, the dopant precursor
may be turned off and the deposition system may be purged with one
or more inert gases to remove the excess dopant precursor.
[0046] In step 420, the helium plasma may be turned on to generate
helium metastable atoms. The substrate in the process chamber may
again be exposed to the helium metastable atoms so that they may
react with the adsorbed dopant precursor thereon to desorb the
non-dopant atoms. For example, for a diborane monolayer, the helium
metastable atoms may help remove the excess hydrogen atoms to form
a desired partial or complete boron monolayer. Exposure of the
substrate surface to the metastable atoms may last, for example,
for a few seconds or up to a few tens of seconds.
[0047] In step 422, the helium plasma may be turned off and the
deposition system may be again purged with one or more inert
gases.
[0048] The above-described process steps of 406 through 412 and/or
the process steps of 416 through 422 may be repeated until a
desired silicon film with one or more monolayers with desired
dopant profile has been obtained.
[0049] It should be understood that, although the above examples
only describe the deposition and/or doping of a silicon film,
embodiments of the present disclosure may be easily adapted to
deposit or dope thin films of other materials or species. For
example, ALD thin films containing the following species may also
be deposited or doped: germanium (Ge), carbon (C), gallium (Ga),
arsenic (As), indium (In), aluminum (Al), or phosphorus (P). The
resulting thin film may contain a single species such as carbon or
germanium, or a compound such as III-V compounds (e.g., GaAs,
InAlP). For this purpose, a precursor substance containing the
corresponding species may be utilized. Candidates for the precursor
substance may include but are not limited to: hydrides (e.g.
SiH.sub.4, Si.sub.2H.sub.6, GeH.sub.4) or halogenated hydrides
(e.g. SiHCl.sub.3), halogenated hydrocarbons (such as CHF.sub.3),
alkyls (e.g. trimethyl aluminum--Al(CH.sub.3).sub.3, or dimethyl
ethyl aluminum--CH.sub.3CH.sub.2--Al(CH.sub.3).sub.2), or halides
(such as CCl.sub.4 or CCl.sub.2F.sub.2).
[0050] The present disclosure is not to be limited in scope by the
specific embodiments described herein. Indeed, other various
embodiments of and modifications to the present disclosure, in
addition to those described herein, will be apparent to those of
ordinary skill in the art from the foregoing description and
accompanying drawings. Thus, such other embodiments and
modifications are intended to fall within the scope of the present
disclosure. Further, although the present disclosure has been
described herein in the context of a particular implementation in a
particular environment for a particular purpose, those of ordinary
skill in the art will recognize that its usefulness is not limited
thereto and that the present disclosure may be beneficially
implemented in any number of environments for any number of
purposes. Accordingly, the claims set forth below should be
construed in view of the full breadth and spirit of the present
disclosure as described herein.
* * * * *